Efficient optical signal amplification systems and methods

ABSTRACT

An optical communication amplification system may include a number of amplification stages for an optical signal that includes a first optical wavelength band signal portion and a second optical wavelength band signal portion. Each amplification stage may separate the first optical wavelength band signal portion from the second optical wavelength band signal portion. The separated first optical wavelength band signal portion is amplified using one or more first optical wavelength band amplifiers and the separated second optical wavelength band signal portion are amplified using one or more second optical wavelength band amplifiers. The amplified first optical wavelength band signal portion is filtered and a reflected portion of the first optical wavelength band signal portion may be used to provide energy to the one or more second optical wavelength band amplifiers to increase the power or gain of the separated second optical wavelength band signal portion.

TECHNICAL FIELD

The present disclosure relates to optical transmission of informationand, more particularly, to systems and methods for self-powering opticaltransmission systems.

BACKGROUND

Long-haul optical communication systems, e.g., optical communicationsystems spanning a distance of greater than about 600 kilometers, sufferfrom signal attenuation resulting from a variety of factors, includingscattering, absorption, and bending. To compensate for attenuation,long-haul systems may include a series of optical amplifiers or“repeaters” spaced along the transmission path between a transmitter anda receiver. The amplifiers amplify the optical signal in a mannerallowing reliable detection at the receiver. Usually, multiple repeatersare positioned along a single fiber optic transmission link, withnumbers reaching more than a hundred per link in submarine systems.Power efficiency of repeaters, particularly those used in submarineapplications, is quite important. For terrestrial systems, increasingefficiency is crucial for reducing amplifier size and cost, includingmaterial and operating costs. For submarine systems increasingefficiency is important to minimize the cost of labor of installingmultiple repeaters in remote, difficult to reach, locations and insupplying energy to the repeaters in such locations.

Erbium doped fiber amplifiers (EDFAs) have proven particularly useful inlong-haul systems. EDFAs include C-band EDFAs and L-band EDFAs which areused to amplify different optical bands, denoted as C-band and L-band.C-band usually includes wavelengths from 1530 nanometers (nm) to 1565 nmand L-band usually includes wavelengths from 1565 nm to 1625 nm. BothC-band and L-band features the lowest attenuation of commonly usedoptical transmission bands, the exact wavelength of the lowestattenuation depends on fiber design and can be in either C or L band.EDFAs may amplify only C-band signals (referred to as a “C-band EDFA”),only L-band signals (referred to as an “L-band EDFA”) or both C-band andL-band signals (referred to as a “C+L EDFA”). Generally, each EDFAincludes nearly independent C-band and L-band amplificationportions—i.e., the amplifier is a combination of two EDFAs: one C-bandEDFA and one L-band EDFA, with economies taken in the form of sharedcomponents within the C+L EDFA. In a C+L EDFA, the input optical signalis usually split between C-band and L-band using a device such as a C+Ldemultiplexer or splitter. The C-band and L-band signals areindependently amplified and recombined using a C+L multiplexer orcombiner. Physically, the splitter and the combiner may be similardevices and the name simply denotes the functionality assigned to thedevice.

Usually, an EDFA is used to produce gain having a particular spectralshape over the signal wavelength band—i.e., over the amplification bandor range of the device. The spectral shape is usually “flat” inasmuch asthe amplification across the wavelength band of the device is eithersimilar or varies linearly with the signal wavelength. The exactamplification shape may be achieved through the use of a Gain FlatteningFilter (GFF).

Several types of GFF exist. One type of GFF uses Short Period FiberBragg Grating (SP-FBG) that is able to provide very accurate shaping ofthe optical signal over the amplification band. Such accuracy isadvantageous in long links that characterize submarine communicationsystems where the number of repeaters is large and errors in the EDFAgain shapes are undesirable. One feature of SP-FBG filters is that thefiltering function is performed by redirecting unneeded light, includingboth signal and amplified spontaneous emission (ASE) noise in thebackward direction—i.e., in a direction opposite the direction ofpropagation of the optical signal. Usually, the back propagated light isundesirable for the upstream EDFAs and is blocked using an isolatorpositioned before the SP-FBG filter.

There is therefore a need for systems and methods of reducing the powerdemand presented by amplifiers along difficult to access opticaltransmission lines such as submarine transmission lines. There is also aneed for systems and methods of beneficially recovering the energypresent in the optical signals reflected by filters such as SP-FBGfilters, particularly along difficult to access optical transmissionlines such as submarine transmission lines.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of various embodiments of the claimed subjectmatter will become apparent as the following Detailed Descriptionproceeds, and upon reference to the Drawings, wherein like numeralsdesignate like parts, and in which:

FIG. 1A is a block diagram of an illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 1B is a block diagram of an alternative illustrative amplificationand reflected signal energy recovery system, in accordance with at leastone embodiment of the present disclosure:

FIG. 1C is a block diagram of another alternative illustrativeamplification and reflected signal energy recovery system, in accordancewith at least one embodiment of the present disclosure;

FIG. 2 is a schematic diagram depicting a number of amplification andreflected signal energy recovery system positioned along a submarineoptical transmission cable, in accordance with at least one embodimentof the present disclosure;

FIG. 3 is a schematic diagram of an illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 4 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure:

FIG. 5 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 6 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 7 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 8 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 9 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 10 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 11 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 12 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 13 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 14 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system, in accordance with at least oneembodiment of the present disclosure;

FIG. 15 is a high-level flow diagram of an illustrative amplificationand reflected signal energy recovery method, in accordance with at leastone embodiment of the present disclosure;

FIG. 16 is a high-level flow diagram of an illustrative amplificationand reflected signal energy recovery method in which a first portion ofan optical signal and a second portion of the optical signal areamplified prior to demultiplexing the optical signal, in accordance withat least one embodiment of the present disclosure;

FIG. 17 is a high-level flow diagram of an illustrative amplificationand reflected signal energy recovery method in which a first portion ofan optical signal is amplified subsequent to demultiplexing the opticalsignal into the first portion and a second portion, in accordance withat least one embodiment of the present disclosure; and

FIG. 18 is a high-level flow diagram of an illustrative amplificationand reflected signal energy recovery method, in accordance with at leastone embodiment of the present disclosure.

Although the following Detailed Description will proceed with referencebeing made to illustrative embodiments, many alternatives, modificationsand variations thereof will be apparent to those skilled in the art.

DETAILED DESCRIPTION

An optical signal may include multiple bands, for example a firstportion that may include a plurality of signals within C-bandwavelengths (1530 nanometers (nm) to 1565 nm) and a second portion thatmay include a plurality of signals within L-band wavelengths (1565 nm to1625 nm). Each of the different wavelength signals may be introducedonto a single core fiber using any current or future developedmultiplexing technology, for example wavelength division multiplexing(WDM). As an optical signal travels along the fiber, significantattenuation may occur over long distances, and may present a significantchallenge to the integrity of the data carried by the optical signal,such as those encountered in submarine communication systems. Amplifiersmay be positioned along such fibers to boost the optical signal andminimize or prevent data loss at the terminal end of the fiber.

As an optical signal is amplified, the amplifier gain needs to becarefully designed controlled. In EDFAs, the gain is provided by pumpedErbium Doped Fiber (EDF), however, the gain shape of the pumped EDF isnot flat and is not the one which is required for the amplifier tocompensate the losses in transmission fiber. To address this issue, mostamplifiers include one or more gain flattening filters (GFFs) tocompensate for the gain differences introduced by EDF in differentchannels and to achieve the overall required gain shape. GFFs can alsobe used to suppress gain outside of the bands of the interest to reduceundesirable amplification of light that does not carry any information.

Certain filter types, such as a Short Period Fiber Bragg Grating(SP-FBG) filter may reflect a portion of the optical signal in the formof unneeded signal and amplified spontaneous emission (ASE) back alongthe fiber. Where the optical signal includes signals in the firstwavelength band (e.g., C-band) and in the second wavelength band (e.g.,L-band), a portion of the energy in the signals reflected by the SP-FBGfilter may be used to pump the L-band portion of a C-band/L-band erbiumdoped fiber amplifier (C+L EDFA). In installations containing a C-bandgain flattening filter (GFF) and an L-band GFF, only the energycontained in the signal reflected from the C-band GFF may be reused forL-band pumping. In implementations using a combined GFF (i.e., a singleGFF for filtering both C-band and L-band), the L-band light may beblocked or otherwise removed and/or dissipated prior to introducing thereflected light to the L-band portion of the EDFA for pumping. Such anarrangement may advantageously increase the efficiency of the EDFAwithout increasing the overall power budget.

An optical communication amplification system is provided. The opticalcommunication amplification system may include an optical splitter toseparate an optical signal into at least a first optical wavelength bandsignal portion and the second optical wavelength band signal portion.The system may further include an optical amplifier operably coupled tothe optical splitter, the optical amplifier to increase the energy ofthe second optical wavelength band signal portion. The system mayadditionally include an optical combiner that combines the first opticalwavelength band signal portion and the amplified second opticalwavelength band signal portion and an optical filter operably coupled tothe optical combiner, wherein a portion of the energy of the firstoptical wavelength band signal portion reflected from the optical filteris received by the optical amplifier where the received energy increasesthe energy of the second optical wavelength band signal portion.

An optical communication amplification method is also provided. Themethod may include splitting an optical signal into a first opticalwavelength band signal portion and a second optical wavelength bandsignal portion and amplifying, via an optical amplifier, the secondoptical wavelength band signal portion of the optical signal. The methodmay further include combining the first optical wavelength band signalportion and the amplified second optical wavelength band signal portionto provide an amplified optical signal and filtering, via at least oneoptical filter, the amplified optical signal. The method mayadditionally include receiving, by the optical amplifier, at least aportion of the first optical wavelength band signal portion reflected bythe at least one optical filter and increasing the energy of the opticalamplifier using energy in the reflected portion of the first opticalwavelength band signal portion.

An optical communication amplification method is also provided. Themethod may include amplifying, by an optical amplifier, an opticalsignal that includes at least a first optical wavelength band signalportion and a second optical wavelength band signal portion. The methodmay further include passing the amplified optical signal through atleast one optical filter, receiving, at the optical amplifier, at leasta portion of energy in the first optical wavelength band signal portionreflected by the at least one optical filter, and increasing the energyof an optical amplifier used to increase the energy level of the secondoptical wavelength signal portion using the reflected energy in thefirst optical wavelength signal portion.

As used herein, the terms “top” and “bottom” are intended to provide arelative and not an absolute reference to a location. Thus, inverting anobject having a “top cover” and a “bottom cover” may place the “bottomcover” on the top of the object and the “top cover” on the bottom of theobject. Such configurations should be considered as included within thescope of this disclosure.

As used herein, the terms “first,” “second,” and other similar ordinalsare intended to distinguish a number of similar or identical objects andnot to denote a particular or absolute order of the objects. Thus, a“first object” and a “second object” may appear in any order—includingan order in which the second object appears before or prior in space ortime to the first object. Such configurations should be considered asincluded within the scope of this disclosure.

FIG. 1A is a block diagram of an illustrative amplification andreflected signal energy recovery system 100, in accordance with at leastone embodiment of the present disclosure. FIG. 1B is a block diagram ofan alternative illustrative amplification and reflected signal energyrecovery system 100, in accordance with at least one embodiment of thepresent disclosure. FIG. 1C is a block diagram of another alternativeillustrative amplification and reflected signal energy recovery system100, in accordance with at least one embodiment of the presentdisclosure.

Referring first to FIG. 1A, in embodiments, an incoming signal 102 mayinclude any number of individual signals within a first portion of theoptical spectrum in combination with (e.g., multiplexed with) any numberof individual signals within a second portion of the optical spectrum.In implementations, the first portion of the optical spectrum maycorrespond to any plurality of frequencies within the optical spectrum,such as the C-band portion of the optical spectrum that includes signalshaving wavelengths between 1530 nanometers (nm) and 1565 nm. In someimplementations, the second portion of the optical spectrum maycorrespond to any plurality of frequencies within the optical spectrum,such as the L-band portion of the optical spectrum that includes signalshaving wavelengths between 1565 nm and 1625 nm.

As depicted in FIG. 1, an oval surrounding a numeral “1” is used todenote the first portion (e.g., the C-band portion) of the opticalspectrum, the size of the oval indicates the relative strength of thefirst portion of the optical spectrum (larger indicating greater signalstrength or energy), and shading within the oval indicates the relativenoise present within the first portion of the optical spectrum (darkercorresponding to greater noise levels). Similarly, an oval surrounding anumeral “2” is used to denote the second portion (e.g., the L-bandportion) of the optical spectrum, the size of the oval indicates therelative strength of the second portion of the optical spectrum (largerindicating greater signal strength or energy), and shading within theoval indicates the relative noise present within the second portion ofthe optical spectrum (darker corresponding to greater noise levels).

Within the amplification and reflected signal energy recovery system100, the signal 102 may be introduced to one or more amplifiers 110. Theone or more amplifiers 110 may include any number and/or combination ofcurrent or future developed optical amplifiers, such as one or moreerbium doped fiber amplifiers. In some implementations, the one or moreamplifiers 110 may amplify both the first portion and the second portionof signal 102. In such implementations, the one or more amplifiers 110may equally or unequally amplify the first portion and the secondportion of the incoming signal 102. In some implementations, the one ormore amplifiers 110 may amplify either the first portion or the secondportion of the incoming signal 102. Regardless of the portion of theoptical spectrum amplified, the one or more amplifiers 110 introduce aquantity of noise into a signal 112 that is output by the one or moreamplifiers 110. As depicted in FIG. 1, the signal 112 provided by theone or more amplifiers 110 may include an amplified first portion of theincoming signal 102 and an amplified second portion of the incomingsignal 102.

The signal 112 from the one or more amplifiers 110 may be introduced toone or more demultiplexers 120. The one or more demultiplexers mayinclude any number and/or combination of current or future developedmultiplexers and/or demultiplexers, for example a three-port orfour-port wavelength division multiplexer (WDM) combiner. Inembodiments, the one or more demultiplexers 120 may separate the firstportion of the signal 112 from the second portion of the signal 112. Theone or more demultiplexers 120 output a signal 122 that includes some orall of the first portion of signal 112 and a signal 124 that includessome or all of the second portion of signal 112.

The output 122 from the demultiplexer 120 containing the second portionof signal 112 may be introduced to one or more amplifiers 130. The oneor more amplifiers 130 may include any number and/or combination ofcurrent or future developed optical amplifiers, such as one or moreerbium doped fiber amplifiers. In some implementations, the one or moreamplifiers 130 may amplify some or all of the second portion of theincoming signal 102. Regardless of the portion of the optical spectrumamplified, the one or more amplifiers 130 introduce a quantity of noiseinto the output 132 produced by the one or more amplifiers 130. Asdepicted in FIG. 1, the one or more amplifiers 130 generate an output132 that includes a further amplified second portion of the incomingsignal 102.

The output 132 from the one or more amplifiers 130 may be introduced toone or more multiplexers 140. Within the one or more multiplexers 140,the amplified second portion of the incoming signal 102 in the output132 received from the one or more amplifiers 130 is combined with theamplified first portion of the incoming signal 102 in the output 124received from the one or more demultiplexers 120. The one or moremultiplexers 140 may include any number and/or combination of current orfuture developed multiplexers, for example a three-port or four-portwavelength division multiplexer (WDM). In embodiments, the one or moremultiplexers 140 may generate an output 142 that includes some or all ofthe amplified first portion of the incoming signal 112 and some or allof the amplified second portion of the incoming signal 102. Havingpassed through the one or more amplifiers 110, the amplified firstportion of the incoming signal 102 received by the one or moremultiplexers 140 may include noise. Having passed through the one ormore amplifiers 110 and the one or more amplifiers 130, the amplifiedsecond portion of the incoming signal 102 may contain noise at a levelexceeding the noise level of the amplified first portion of the incomingsignal 102.

One or more filters 160 receive the output 142 from the one or moremultiplexers 140 via one or more optical circulators 150. The one ormore optical circulators 150 may include any number and/or combinationcurrent or future developed devices and/or systems capable of separatingoptical signals traveling in opposite directions along an optical fiber.In some implementations, the one or more optical circulators 150 mayinclude a three-port device in which an optical signal entering a firstport exits via the next sequential port (i.e., an optical signalentering port 1 exits via port 2 and an optical signal entering via port2 exits via port 3). In some implementations, the one or morecirculators 150 may provide a high level of isolation between the inputoptical signal and a reflected optical signal. In some implementations,the one or more circulators 150 may provide relatively low insertionlosses within the amplification and reflected signal energy recoverysystem 100.

The one or more filters 160 may include any number and/or combinationcurrent or future developed devices and/or systems capable of separatingor otherwise removing at least one optical wavelength from a largerplurality of optical wavelengths. In some implementations, the one ormore filters 160 may include a number of gain flattening filters (GFF).In some implementations, the one or more filters 160 may include anumber of Short Period Fiber Bragg Grating (SP-FBG) filters capable ofproviding accurate shaping of the output 142 from the one or moreoptical circulators 150 over the amplification band of the one or moreamplifiers 110, the one or more amplifiers 130, or combinations thereof.In at least some implementations, the one or more filters 160 mayproduce an output signal 162 that includes at least the filtered andamplified first portion of the incoming signal 102 and at least thefiltered and amplified second portion of the incoming signal 102. Insome implementations, the filtered and amplified first portion of theincoming signal 102 included in the output signal 162 may have an energylevel greater than the energy level of the first portion of the incomingsignal 102 received by the one or more amplifiers 110. In someimplementations, the filtered and amplified second portion of theincoming signal 102 included in the output signal 162 may have an energylevel greater than the energy level of the second portion of theincoming signal 102 received by the one or more amplifiers 110.

In operation, the one or more filters 160 reflect at least a portion ofthe energy included in the amplified first portion of the incomingsignal 102. In FIG. 1, this reflected portion of the amplified firstportion of the incoming signal 102 is depicted as an oval containing anitalicized numeral “1.” The one or more circulators 150 provide anoutput 164 that includes at least a portion of the energy contained inthe amplified first portion of the incoming signal 102 reflected by theone or more filters 160. The output 164, containing the portion of theenergy contained in the amplified first portion of the incoming signal102 reflected by the one or more filters 160 may be directed to the oneor more amplifiers 130 where at least some of the energy may be used toamplify or increase the energy level of the second portion of theincoming signal 102.

Referring now to FIG. 1B, the one or more amplifiers 110 upstream of theone or more demultiplexers 120 have been removed. The signal 102 nowfirst enters the one or more demultiplexers 120. The output 124 of theone or more demultiplexers 120 includes the first portion of signal 102.One or more amplifiers 170 receive the first portion of signal 102 andoutput 172 an amplified first portion of signal 102. The one or moreamplifiers 170 may include any number and/or combination of current orfuture developed optical amplifiers, such as one or more erbium dopedfiber amplifiers. In some implementations, the one or more amplifiers170 may amplify only the first portion of signal 102. The one or moreamplifiers 170 introduce a quantity of noise into the signal 172 that isoutput by the one or more amplifiers 170. The remainder of theamplification and reflected signal energy recovery system 100 depictedin FIG. 1B remains similar to that depicted in FIG. 1A.

Referring now to FIG. 1C, the one or more demultiplexers 120 provide anoutput 124 that includes the first portion of signal 102. The output 124is introduced to one or more amplifiers 170 prior to being introduced toone or more multiplexers 140. The remainder of the amplification andreflected signal energy recovery system 100 depicted in FIG. 1C remainssimilar to that depicted in FIGS. 1A and 1B.

FIGS. 1A-IC demonstrate the beneficial recovery and reuse of energycontained in the amplified first portion of the incoming signal 102reflected by the one or more filters 160 back to the one or morecirculators 150. Such energy recovery and reuse may advantageouslyreduce the quantity of energy consumed by the amplification andreflected signal energy recovery system 100.

Turning now to FIG. 2, there is illustrated an exemplary opticalcommunication system 200 that includes a number of amplification andreflected signal energy recovery systems 100A-100 n positioned atregular or irregular intervals along a submarine optical transmissioncable 224, in accordance with at least one embodiment of the presentdisclosure. Those skilled in the art will recognize that the system 200has been depicted as a highly simplified point-to-point system for easeof explanation. It is to be understood the present invention may beincorporated into a wide variety of optical networks and systems.

The illustrated exemplary optical communication system 200 includes atransmitter 202 and a receiver 206 connected via an optical transmissionpath 204. At the transmitter 202, a plurality of separate opticalsignals may be generated by modulating data on each of a plurality ofdifferent wavelengths/channels within a signal bandwidth. Thetransmitter 202 may combine the separate channels into an aggregateoptical signal and transmit the aggregate optical signal over theoptical information path 204 to the receiver 206. Although the system200 is illustrated as including a distinct transmitter 202 and receiver206, those of ordinary skill in the art will recognize the transmitter202 and receiver 206 may each be configured as a transceiver tofacilitate bi-directional communication over the optical informationpath.

Depending on system characteristics and requirements, the opticaltransmission path 204 may include, optical transmission fiber 210,amplification and reflected signal energy recovery systems 100-1 through100-N consistent with the present invention, optical filters, and otheractive and passive components. For clarity, only optical amplifiers100-1, 100-2, 100-3, 100-(N−1), 100-N and optical transmission fiber 210are illustrated in the optical information path 204. Optical amplifierconfigurations consistent with the present invention will be describedin greater detail herein. Configurations for other components includedin the transmission path are known to those of ordinary skill in theart.

System 200 may be configured as a long-haul system, e.g. having a lengthfrom the transmitter to receiver of more than about 600 km, and may spana body of water 212. When used to span a body of water, e.g. an ocean,optical amplifiers 100-1, 100-2, 100-3, 100-(N−1). 100-N may be seatedon the ocean floor 214 and the transmission path 204 may span betweenbeach landings 216, 218 to extend from the water 212 for coupling to thetransmitter 202 and receiver 206. It will be appreciated that aplurality of optical transmission components may be coupled to thetransmission path 204 and may be disposed beneath water and/or overland.

In general, the distance between optical amplifiers defines atransmission span length. The illustrated exemplary embodiment includesa plurality of spans, 224-1, 224-2, 223-3 . . . 224-(I−1), 224-I. Thoseor ordinary skill in the art will recognize that span lengths may varysignificantly in a particular system. In a long-haul system, forexample, some spans may be as short as 20 kilometers, while some spansmay exceed 100 km. In view of the span length variation, signalattenuation varies from span-to-span.

FIG. 3 is a schematic diagram of an illustrative amplification andreflected signal energy recovery system 300, in accordance with at leastone embodiment of the present disclosure. An optical isolator 302receives the incoming signal 102. In embodiments, the incoming signal102 may include at least a first optical wavelength band signal portion102A and a second optical wavelength band signal portion 102B. Inembodiments, the first optical wavelength band signal portion 102A mayinclude some or all of the wavelengths included in the C-band portion ofthe optical spectrum (1530 nm to 1565 nm). In embodiments, the secondoptical wavelength band signal portion 102B may include some or all ofthe wavelengths included in the L-band portion of the optical spectrum(1565 nm to 1625 nm). The optical isolator 302 permits the passage ofthe incoming optical signal 102 in a first direction and prevents thepassage of any optical signal in the reverse (i.e., the incoming)direction. The optical isolator 302 may include any number and/orcombination current or future devices and/or systems capable ofpermitting the passage of an optical signal in a first direction andblocking the passage of an optical signal in a second direction.

One or more amplifiers 306 may receive the output 304 from the opticalisolator 302. In embodiments, the one or more amplifiers 306 may amplifysome or all of the wavelengths in the first optical wavelength bandsignal portion 102A, some or all of the wavelengths in the secondoptical wavelength band signal portion 102B, or any combination thereof.In some implementations, the one or more amplifiers 306 may be selected,operated, and/or tuned such that the gain of at least the first opticalwavelength band signal portion 102A is sufficiently great that noadditional amplification of the first optical wavelength band signalportion 102A is needed. In embodiments, the one or more amplifiers 306may be selected, operated, and/or tuned such that the gain of at leastthe second optical wavelength band signal portion 102B is insufficientand additional amplification of the second optical wavelength bandsignal portion 102B may be desirable.

In embodiments, the one or more amplifiers 306 may include one or moreerbium doped fiber amplifiers (EDFAs). Each of the EDFAs may include asingle or multi-stage EDFA, and may include one or more EDFA pumpsources 308, a coupler 310, and an erbium-doped fiber segment 312.Various configurations for EDFA pump sources that may be controlledlocally or remotely are known to those of ordinary skill in the art.Also, the pump sources may be coupled to the optical path 304 in a knownconfiguration.

One or more type-1 signal splitter/combiners 316 receive the output 314from the one or more amplifiers 306. Each type-1 signalsplitter/combiner 316 may be identified in the figures by a small “T-1”designation that appears in the upper right-hand portion of the iconused to represent signal splitter 316. Each type-1 signal splitter 316may be used to separate (i.e., demultiplex) or combine (i.e., multiplex)a number of optical signals. Each type-1 signal splitter/combiner 316may be based on a dielectric thin film filter (TFF). The iconrepresenting the type-1 signal splitter 316 depicts the thin film layerdisposed within the signal splitter in a manner that represents onepossible embodiment of such a device.

As used herein, each type-1 signal splitter/combiner 316 transmits thefirst optical wavelength band signal portion 102A and reflects thesecond optical wavelength band signal portion 102B. Thus, output 318from the one or more type-1 signal splitter/combiners 316 may includesome or all of the second optical wavelength band signal portion 102B ofthe incoming signal 102 and output 320 includes some or all of the firstoptical wavelength band signal portion 102A of the incoming signal 102.

The second optical wavelength band signal portion 102B passes throughone or more optical isolators 322 each of which permit theunidirectional passage of optical signals. One or more amplifiers 326may receive the output 324 of the one or more optical isolators 322. Inembodiments, the one or more amplifiers 326 may amplify some or all ofthe wavelengths in the second optical wavelength band signal portion102B. In some implementations, the one or more amplifiers 326 may beselected, operated, and/or tuned such that no additional amplificationof the second optical wavelength band signal portion 102B is needed.

In embodiments, the one or more amplifiers 326 may include one or moreerbium doped fiber amplifiers (EDFAs). Each of the EDFAs may include asingle or multi-stage EDFA, and may include one or more EDFA pumpsources 328, a coupler 330, and an erbium-doped fiber segment 332.Various configurations for EDFA pump sources that may be controlledlocally or remotely are known to those of ordinary skill in the art.Also, the pump sources may be coupled to the optical path 324 in anyknown configuration.

One or more type-2 signal splitter/combiners 334 may receive the outputfrom the one or more amplifiers 326. Each type-2 signalsplitter/combiner 334 may be identified in the figures by a small “T-2”designation that appears in the upper right-hand portion of the iconused to represent the type-2 signal splitter/combiner 334. Each type-2signal splitter/combiner 334 may be used to separate (i.e., demultiplex)or combine (i.e., multiplex) a number of optical signals. Each type-2signal splitter/combiner 334 may be based on a dielectric thin filmfilter (TFF) that reflects one or more portions of the optical spectrumand transmits one or more other portions of the optical spectrum. Theicon representing the type-2 signal splitter/combiner 334 depicts thethin film layer disposed within the signal splitter in a manner thatrepresents one possible embodiment of such a device.

As used herein, each type-2 signal splitter/combiner 334 transmits thesecond optical wavelength band signal portion 102B and reflects thefirst optical wavelength band signal portion 102A. Thus, output 336 fromthe one or more type-2 signal splitter/combiners 334 includes some orall of both the first optical wavelength band signal portion 102A (i.e.,output 320 from the one or more type-1 splitters 316) and some or all ofthe second optical wavelength band signal portion 102B (i.e., outputfrom the one or more amplifiers 326).

One or more optical circulators 338 may receive the output 336 from theone or more type-2 signal splitter/combiners 334. The one or moreoptical circulators 338 separate optical signals travelling in differentdirections along an optical fiber. As depicted in FIG. 3, the one ormore optical circulators 338 is a three-port device designed such thatan optical signal entering one port exits from the next port asidentified by the directional arrows within the optical circulator icon.

One or more gain flattening filters (GFF) 342 receive the output 340from the one or more optical circulators 338. In at least someimplementations, the output 340 may include all or a portion of thefirst optical wavelength band signal portion 102A and all or a portionof the second optical wavelength band signal portion 102B. The one ormore GFFs 342 pass optical signals falling within the first opticalwavelength band signal portion 102A and the second optical wavelengthband signal portion 102B and reject optical signals falling outsideeither the first optical wavelength band signal portion 102A or thesecond optical wavelength band signal portion 102B.

In at least some implementations, the one or more GFFs 342 may includeone or more Short Period Fiber Bragg Grating (SP-FBG) filters capable ofproviding accurate shaping of the output 340 from the one or moreoptical circulators 338. In at least some implementations, the one ormore GFFs 342 may produce an output signal 346 that includes at leastthe filtered and amplified first optical wavelength band signal portion102A and at least the filtered and amplified second optical wavelengthband signal portion 102B.

In some implementations, the one or more GFFs 342 may reflect a portionof the incident signals as a reflected output signal 344 that isdirected in a reverse direction, back toward the one or more opticalcirculators 338. The reflected output signal 344 may include energy inthe form of reflected optical signals in the first optical wavelengthband signal portion 102A and/or the second optical wavelength bandsignal portion 102B. In addition, the reflected output signal 344 mayinclude energy in the form of amplified spontaneous emission (ASE)noise.

The one or more optical circulators 338 receive the reflected outputsignal 344 from the one or more GFFs 342 and pass the reflected opticalsignal to the one or more type-2 signal splitter/combiners 334. The oneor more type-2 signal splitter/combiners 334 reflect the opticalwavelengths in the first optical wavelength band signal portion 102A anddirect the reflected optical wavelengths in the first optical wavelengthband signal portion 102A to the one or more amplifiers 326. The one ormore amplifiers 326 may use at least a portion of the energy in thereflected first optical wavelength band signal portion 102A to increasethe energy of the second optical wavelength band signal portion 102Bintroduced to the one or more amplifiers 326 via the output signal 318.

The output 346 from the one or more GFFs 342 includes an amplified firstoptical wavelength band signal portion 102A and an amplified secondoptical wavelength band signal portion 102B. One or more opticalisolators 348 receives the output 346 from the one or more GFFs 342 andpasses the output as output signal 162. The output signal 162 exitingthe one or more optical isolators 348 includes the amplified firstoptical wavelength band signal portion 102A and the amplified secondoptical wavelength band signal portion 102B.

FIG. 4 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 400, in accordance with at leastone embodiment of the present disclosure. As depicted in FIG. 4, the oneor more type-2 signal splitter/combiners 334 directly receive theoptical signal 344 reflected by the one or more GFFs 342. The reflectedoutput 408 from the one or more type-2 signal splitter/combiners 334includes at least a portion of the reflected first optical wavelengthband signal portion 102A_(r). Note that in FIGS. 4 through 14 elementsmay be referred to in the singular, such should be considered torepresent one or more of the elements as may be required by the systemdepicted in the respective figure.

The optical circulator 402 receives the reflected first opticalwavelength band signal portion 102A_(r) and outputs 404 all or a portionof the reflected first optical wavelength band signal portion 102A_(r).

The optical circulator 406 receives the reflected first opticalwavelength band signal portion 102A_(r) from the optical circulator 402and outputs at least a portion of the reflected first optical wavelengthband signal portion 102A_(r) to the amplifier 326. The amplifier 326 mayadd at least a portion of the energy in the reflected first opticalwavelength band signal portion 102A_(r) to the second optical wavelengthband signal portion 102B.

FIG. 5 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 500, in accordance with at leastone embodiment of the present disclosure. As depicted in FIG. 5, theoptical circulator 338 receives the optical signal 344 reflected by theGFF 342. In embodiments, the optical signal 344 reflected by the GFF 342may include a reflected portion of the first optical wavelength bandsignal portion 102A_(r), a reflected portion of the second opticalwavelength band signal portion 102B_(r), and amplified spontaneousemission (ASE) noise rejected by the one or more GFFs 342.

The output 502 from the optical circulator 338 is returned to afour-port, type-1, optical splitter/combiner 504. Output 506 from thefour-port, type-1, optical splitter/combiner 504 may include thereflected portion of the second optical wavelength band signal portion102B included in the incoming signal 102 and at least a portion of thereflected first optical wavelength band signal portion 102A_(r). Thereflected first optical wavelength band signal portion 102A_(r) passesthrough the isolator 322 and is received by the amplifier 326. At leasta portion of the energy carried by the reflected first opticalwavelength band signal portion 102A_(r) may then be used by theamplifier 326 to boost the gain of the second optical wavelength bandsignal portion 102B of the incoming signal 102.

FIG. 6 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 600, in accordance with at leastone embodiment of the present disclosure. As depicted in FIG. 6, theincoming signal 102 is split into at least the first optical wavelengthband signal portion 102A and the second optical wavelength band signalportion 102B prior to amplification. The type-1 splitter/combiner 316receives the unamplified incoming signal 102. The output 602 from thetype-1 splitter/combiner 316 may include at least the first opticalwavelength band signal portion 102A. The output 318 from the type-1splitter/combiner 316 may include at least the second optical wavelengthband signal portion 102B.

The amplifier 604 receives the output 602. The output 602 may include atleast the first optical wavelength band signal portion 102A, from thetype-1 splitter/combiner 316. In embodiments, the amplifier 602 mayamplify some or all of the wavelengths in the first optical wavelengthband signal portion 102A. In some implementations, the amplifier 306 maybe selected, operated, and/or tuned such that the gain of at least thefirst optical wavelength band signal portion 102A is sufficientlyincreased such that no additional amplification of the first opticalwavelength band signal portion 102A is needed.

In embodiments, the amplifier 604 may include an erbium doped fiberamplifier (EDFA). In embodiments, each EDFA may include either asingle-stage EFDA or multi-stage EDFA, and may include an EDFA pumpsource 606, a coupler 608, and an erbium-doped fiber segment 610.Various control configurations for the EDFA pump source 606, includinglocal or remote control, are known to those of ordinary skill in theart. Also, the pump source 606 may be coupled to the optical path 602 inany known configuration.

The optical circulator 614 receives the output 612 from the amplifier604. The optical circulator 614 may pass at least a portion of the firstoptical wavelength band signal portion 102A received from the amplifier604 to the three-port, type-2, splitter/combiner 334.

In embodiments, the reflected optical signal 344 produced by the GFF 342may include a reflected portion of the first optical wavelength bandsignal portion 102A_(r), a reflected portion of the second opticalwavelength band signal portion 102B_(r), and amplified spontaneousemission (ASE) noise rejected by the GFF 342.

The three-port, type-2, splitter/combiner 334 receives the reflectedfirst optical signal 344 from the GFF 342. The three-port, type-2,splitter/combiner 334 reflects at least a portion of the reflected firstoptical wavelength band signal portion 102A_(r) back to the opticalcirculator 614. The optical circulator 614 provides an output 616 thatincludes at least a portion of the received reflected first opticalwavelength band signal portion 102A_(r).

The optical circulator 618 may receive at least a portion of the output616 from the optical circulator 614. The optical circulator 618 providesan output that includes at least a portion of the reflected firstoptical wavelength band signal portion 102A_(r) to the amplifier 326.

The amplifier 326 receives the reflected first optical wavelength bandsignal portion 102A_(r). In embodiments, the amplifier 326 may use atleast a portion of the energy carried by the reflected first opticalwavelength band signal portion 102A_(r) to increase the gain of thesecond optical wavelength band signal portion 102B received from thetype-1 optical splitter/combiner 316.

FIG. 7 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 700, in accordance with at leastone embodiment of the present disclosure. As depicted in FIG. 7, theamplifier 702 receives the input signal 102. The input signal 102 mayinclude at least the first optical wavelength band signal portion 102Aand the second optical wavelength band signal portion 102B.

In embodiments, the amplifier 702 may amplify some or all of thewavelengths in the first optical wavelength band signal portion 102A,some or all of the wavelengths in the second optical wavelength bandsignal portion 102B, or any combination thereof. In someimplementations, the amplifier 702 may be selected, operated, and/ortuned such that the gain of at least the first optical wavelength bandsignal portion 102A is insufficient and additional amplification of thefirst optical wavelength band signal portion 102A may be desirable. Inembodiments, the amplifier 702 may be selected, operated, and/or tunedsuch that the gain of at least the second optical wavelength band signalportion 102B is insufficient and additional amplification of the secondoptical wavelength band signal portion 102B may be desirable. Inembodiments, the amplifier 702 may include an erbium doped fiberamplifier (EDFA). Each EDFA may consist of either a single-stage EDFA ora multi-stage EDFA, and may include a coupler 704, and an erbium-dopedfiber segment 706.

In some implementations, the amplifier 702 may be operably coupled to asingle EDFA pump source 708 that includes an EDFA pump 710 and anoptical splitter 712 may be used to power at least the amplifier 702.Various configurations for EDFA pump sources that may be controlledlocally or remotely are known to those of ordinary skill in the art.Also, the pump sources may be coupled to the optical path in any knownconfiguration. The optical isolator 720 may receive at least a portionof the output provided by the amplifier 702.

In embodiments, the three-port, type-1 optical splitter/combiner 316 mayreceive the amplified input signal 102 from the optical isolator 720.The amplifier 714 may receive all or a portion of the output 320 fromthe three-port, type-1, optical splitter/combiner 316. The output 320may include at least the first optical wavelength band signal portion102A of incoming signal 102.

In embodiments, the amplifier 714 may amplify some or all of thewavelengths in the first optical wavelength band signal portion 102A. Insome implementations, the amplifier 714 may be selected, operated,and/or tuned such that the gain of at least the first optical wavelengthband signal portion 102A sufficient and additional amplification of thefirst optical wavelength band signal portion 102A may be unnecessary. Inembodiments, the amplifier 714 may include at least one erbium dopedfiber amplifier (EDFA). Each EDFA may consist of either a single-stageEDFA or a multi-stage EDFA, and may include a coupler 716, and anerbium-doped fiber segment 718.

In some implementations, the amplifier 714 may be operably coupled to asingle EDFA pump source 708 that includes at least one EDFA pump 710 andan optical splitter 712 may be used to power the amplifier 702. Variousconfigurations for EDFA pump sources that may be controlled locally orremotely are known to those of ordinary skill in the art. Also, the pumpsources may be coupled to the optical path in any known configuration.In some implementations, the optical isolator 722 may receive at least aportion of the amplified first optical wavelength band signal portion102A provided by the amplifier 714.

In embodiments, the amplifier 326 receives the reflected first opticalwavelength band signal portion 102A_(r) via the type-2 opticalsplitter/combiner 334. In embodiments, the amplifier 326 may use atleast a portion of the energy carried by the reflected first opticalwavelength band signal portion 102A_(r) to increase the gain of thesecond optical wavelength band signal portion 102B received from thetype-1 optical splitter/combiner 316.

FIG. 8 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 800, in accordance with at leastone embodiment of the present disclosure. As depicted in FIG. 8, theamplifier 306 may increase the gain of the incoming signal 102 prior tosplitting the first optical wavelength band signal portion 102A from thesecond optical wavelength band signal portion 102B. After splitting, theamplifier 804 may increase the gain of the first optical wavelength bandsignal portion 102A and the amplifier 326 may increase the gain of thesecond optical wavelength band signal portion 102B.

In embodiments, the amplifier 306 may amplify some or all of thewavelengths in the first optical wavelength band signal portion 102A,some or all of the wavelengths in the second optical wavelength bandsignal portion 102B, or any combination thereof. In someimplementations, the amplifier 306 may be selected, operated, and/ortuned such that the gain of at least the first optical wavelength bandsignal portion 102A is insufficient and additional amplification of thefirst optical wavelength band signal portion 102A may be desirable. Inembodiments, the amplifier 306 may be selected, operated, and/or tunedsuch that the gain of at least the second optical wavelength band signalportion 102B is insufficient and additional amplification of the secondoptical wavelength band signal portion 102B may be desirable.

The amplifier 804 may receive all or a portion of the output 320 fromthe type-1 optical signal splitter/combiners 316. In embodiments, theamplifier 804 may amplify some or all of the wavelengths in the firstoptical wavelength band signal portion 102A. In some implementations,the amplifier 804 may be selected, operated, and/or tuned such that noadditional amplification of the first optical wavelength band signalportion 102A is needed.

In embodiments, the amplifier 804 may include at least one erbium dopedfiber amplifier (EDFA). Each EDFA may consist of either a single-stageEDFA or a multi-stage EDFA, and may include at least one EDFA pumpsource 806, a coupler 808, and an erbium-doped fiber segment 810.Various configurations for EDFA pump sources that may be controlledlocally or remotely are known to those of ordinary skill in the art.Also, the pump sources may be coupled to the optical path 320 in anyknown configuration.

The amplifier 326 receives at least a portion of the reflected firstoptical wavelength band signal portion 102A_(r) via the type-2splitter/combiner 334, optical circulator 402, and optical circulator406. In embodiments, the amplifier 326 may use at least a portion of theenergy carried by the reflected first optical wavelength band signalportion 102A_(r) to increase the gain of the second optical wavelengthband signal portion 102B received from the type-1 opticalsplitter/combiner 316.

FIG. 9 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 900, in accordance with at leastone embodiment of the present disclosure. As depicted in FIG. 9, theamplifier 306 may increase the gain of the incoming signal 102 prior tosplitting the first optical wavelength band signal portion 102A from thesecond optical wavelength band signal portion 102B. After splitting, theamplifier 804 may increase the gain of the first optical wavelength bandsignal portion 102A and the amplifier 326 may increase the gain of thesecond optical wavelength band signal portion 102B. In addition, thesplit first optical wavelength band signal portion 102A may be passedthrough a first gain flattening filter (GFF) 904 and the split secondoptical wavelength band signal portion 102B may be passed through asecond gain flattening filter (GFF) 910. Such an arrangement mayadvantageously permit the selection of at least one GFF 904demonstrating favorable bandpass characteristics for the first opticalwavelength band signal portion 102A and at least one GFF 910demonstrating favorable bandpass characteristics for the second opticalwavelength signal portion 102B. As depicted in FIG. 9, the filtered,amplified, first optical wavelength band signal portion 102A and thefiltered, amplified second optical wavelength band signal portion 102Bmay be combined to provide the output signal 162.

In embodiments, the split first optical wavelength band signal portion102A may pass through an optical circulator 906 prior to reaching theGFF 904. The GFF 904 may pass optical signals falling within the firstoptical wavelength band signal portion 102A and may reject or otherwiseattenuate optical signals falling outside the first optical wavelengthband signal portion 102A.

In at least some implementations, the GFF 904 may include one or moreShort Period Fiber Bragg Grating (SP-FBG) filters capable of providingaccurate shaping of the output 320 from the optical circulators 906. Inat least some implementations, the output signal from the GFF 904 may bepassed to the optical isolators 902.

In some implementations, the GFF 904 may reflect a portion of theincident signal as a reflected output signal 920 that is directed in areverse direction, back toward the optical circulator 906. The reflectedoutput signal 920 may include energy in the form of reflected opticalsignals in the first optical wavelength band signal portion 102A and mayinclude additional energy in the form of amplified spontaneous emission(ASE) noise.

The optical circulator 906 separates optical signals travelling indifferent directions along an optical fiber. As depicted in FIG. 9, inembodiments, the optical circulator 906 may include a three-port devicedesigned such that an optical signal entering one port exits from thenext port as identified by the directional arrows within the opticalcirculator icon.

The reflected first optical wavelength band signal portion 102A_(r)enters the optical circulator 906. All or a portion of the reflectedfirst optical wavelength band signal portion 102A_(r) exits the opticalcirculator 904 as an output 922 which is subsequently introduced to theoptical circulator 908. The optical circulators 908 output the reflectedfirst optical wavelength band signal portion 102A_(r) to the amplifier326 used to increase the gain of at least the second optical wavelengthband signal portion 102B. Within the amplifier 326, some or all of theenergy carried by the reflected first optical wavelength band signalportion 102A_(r) may be used to boost the gain of the second opticalwavelength band signal portion 102B, thereby beneficially reducing theenergy consumption of the amplifier 326 by a commensurate amount.

In embodiments, the split second optical wavelength band signal portion102B may pass through the optical circulator 908 to the GFF 910. The GFF910 may pass optical signals falling within the second opticalwavelength band signal portion 102B and may reject or otherwiseattenuate optical signals falling outside the second optical wavelengthband signal portion 102B.

In at least some implementations, the GFF 910 may include at least oneShort Period Fiber Bragg Grating (SP-FBG) filters capable of providingaccurate shaping of the second optical wavelength band signal portion102B. In at least some implementations, the output signal from the GFF904 may be passed to the type-2 optical signal splitter/combiner 342where the amplified, filtered, first optical wavelength band signalportion 102A is combined with the amplified, filtered, second opticalwavelength band signal portion 102B.

FIG. 10 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 1000, in accordance with atleast one embodiment of the present disclosure. As depicted in FIG. 10,the amplifier 702 may increase the gain of the incoming signal 102 priorto splitting the first optical wavelength band signal portion 102A fromthe second optical wavelength band signal portion 102B. After splitting,the first optical wavelength band signal portion 102A may be filteredusing at least one gain flattening filter (GFF) 904 and amplified usingat least one amplifier 804. After splitting, the second opticalwavelength band signal portion 102B may be amplified using at least oneamplifier 1010 and filtered using at least one gain flattening filter(GFF) 910. Such an arrangement may advantageously permit the selectionof a GFF 904 demonstrating favorable bandpass characteristics for thefirst optical wavelength band signal portion 102A and a GFF 910demonstrating favorable bandpass characteristics for the second opticalwavelength signal portion 102B. As depicted in FIG. 10, the filtered,amplified, first optical wavelength band signal portion 102A and thefiltered, amplified second optical wavelength band signal portion 102Bmay be combined to provide the output signal 162.

As depicted in FIG. 10, the input signal 102 may be amplified using oneor more amplifiers 702 prior to splitting. A four-port, type-1, opticalsignal splitter/combiner 1002 may receive the amplified input signal 102from the amplifier 702. All or a portion of the first optical wavelengthband signal portion 102A may exit the four-port, type-1, optical signalsplitter/combiner 1002 via output 320. All or a portion of the secondoptical wavelength band signal portion 102B may exit the four-port,type-1, optical signal splitter/combiner 1002 via output 318.

The first optical wavelength band signal portion 102A exits thefour-port, type-1, optical signal splitter/combiners 1002, passesthrough the three-port circulator 1004 and the GFF 904. The GFF 904 maypass optical signals falling within the first optical wavelength bandsignal portion 102A and may reject or otherwise attenuate opticalsignals falling outside the first optical wavelength band signal portion102A.

The portion of the first optical wavelength band signal portion 102A_(r)reflected by the GFF 904 enters the optical circulator 1004. The opticalcirculator 1004 separates the reflected first optical wavelength bandsignal portion 102A_(r) and forwards the reflected first opticalwavelength band signal portion 102A_(r) via output 1006 to thefour-port, type-1, optical signal splitter/combiner 1002. The four-port,type-1, optical signal splitter/combiner 1002 combines the reflectedfirst optical wavelength band signal portion 102A_(r) with the splitsecond optical wavelength band signal portion 102B and forwards, viaoutput 318, the combined reflected first optical wavelength band signalportion 102A_(r) and second optical wavelength band signal portion 102Bto the amplifier 1010.

The amplifier 1010 uses at least a portion of the energy carried by thereflected first optical wavelength band signal portion 102A_(r) toamplify or otherwise increase the gain of the second optical wavelengthband signal portion 102B. The amplified second optical wavelength bandsignal portion 102B exits the amplifier 1010, passes through the opticalisolator 1016, through the GFF 910, and enters the type-2 optical signalsplitter/combiner 342. Within the type-2 optical signalsplitter/combiner 342 the amplified first optical wavelength band signalportion 102A and the amplified second optical wavelength band signalportion 102B are combined to provide output signal 162.

FIG. 11 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 1100, in accordance with atleast one embodiment of the present disclosure. As depicted in FIG. 11,the output from the amplifier 326 may pass through a three-port, type-2,optical signal splitter/combiner 1102 and through a sequentialthree-port, type-2, optical signal splitter/combiner 334. The firstoptical wavelength band signal portion 102A_(r) and the second opticalwavelength band signal portion 102B_(r) reflected from the one or moreGFFs 342 is introduced to the three-port, type-2, optical signalsplitter/combiner 1102 where the first optical wavelength band signalportion 102A_(r) is reflected back to the amplifier 326. At least aportion of the energy carried by the reflected first optical wavelengthband signal portion 102A_(r) may be used by the amplifier 326 to amplifyor otherwise boost the gain of the second optical wavelength band signalportion 102B.

FIG. 12 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 1200, in accordance with atleast one embodiment of the present disclosure. As depicted in FIG. 12,the amplified first optical wavelength band signal portion 102A exitsthe three-port, type-1, optical signal splitter/combiner 316 via output320 and enters a four-port optical circulator 1202. The amplified firstoptical wavelength band signal portion 102A exits the four-port opticalcirculator 1202 via output 1204, and enters the three-port, type-2,optical signal splitter/combiner 338.

Also as depicted in FIG. 12, the first optical wavelength band signalportion 102A_(r) reflected by the GFF 342 enters the three-port, type-2,optical signal splitter/combiner 338 where it is reflected back to thefour-port optical circulator 1202. The reflected first opticalwavelength band signal portion 102A_(r) exits the four-port opticalcirculator 1202 via output 1208 and enters the amplifier 326 where atleast a portion of the energy carried by the reflected first opticalwavelength band signal portion 102A_(r), may be used to amplify orotherwise increase the gain of the second optical wavelength band signalportion 102B.

Also as depicted in FIG. 12, the amplified second optical wavelengthband signal portion 102B exits the amplifier 326 and enters thefour-port optical circulator 1202 via output 1208. The amplified secondoptical wavelength band signal portion 102B exits the four-port opticalcirculator 1202 via output 1206 and enters the three-port, type-2,optical signal splitter/combiner 338 where it is combined with theamplified first optical wavelength band signal portion 102A to providethe output signal 162.

FIG. 13 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 1300, in accordance with atleast one embodiment of the present disclosure. As depicted in FIG. 13,the output from the amplifier 306 passes through the three-port, type-2,optical signal splitter/combiner 316. The first optical wavelength bandsignal portion 102A passes through the optical circulator 906 and theGFF 904. The GFF 904 may be selected to pass optical frequencies withinthe first optical wavelength band signal portion 102A and reject otheroptical frequencies. A portion of the first optical wavelength bandsignal portion 102A_(r) is reflected by the filter and enters theoptical circulator via 1302. The reflected portion of the first opticalwavelength band signal portion 102A_(r) exits the optical circulator 906via 1304 and enters the circulator 908. The portion of the first opticalwavelength band signal portion 102A_(r) exits the optical circulator 908and enters the amplifier 702, where at least a portion of the energycarried by the reflected portion of the first optical wavelength bandsignal portion 102A_(r) may be used to amplify or otherwise boost thegain of the second optical wavelength band signal portion 102B thatexits the three-port, type-2, optical signal splitter/combiner 316 via318.

After passing through the optical isolator 322 and the optical amplifier702, the second optical wavelength band signal portion 102B passesthrough at least one GFF 1312. In some implementations, the GFF 1312 maybe selected to pass optical frequencies falling within the secondoptical wavelength band signal portion 102B and block at least a portionof the remaining frequencies outside of the second optical wavelengthband signal portion 102B. In some implementations, the reflected portionof the second optical wavelength band signal portion 102B_(r) may beblocked using an optical isolator 1310.

The filtered and amplified first optical wavelength band signal portion102A and the filtered and amplified second optical wavelength bandsignal portion 102B pass through the three-port, type-2, optical signalsplitter/combiner 334 and the optical isolator 348 before exiting theamplifier 100 as an amplified, filtered, signal 162 that includes boththe first optical wavelength band signal portion 102A and the secondoptical wavelength band signal portion 102B.

FIG. 14 is a schematic diagram of another illustrative amplification andreflected signal energy recovery system 1400, in accordance with atleast one embodiment of the present disclosure. As depicted in FIG. 14,the output from the amplifier 306 may pass through the three-port,type-2, optical signal splitter/combiner 316. The first opticalwavelength band signal portion 102A then enters the four-port, type-2,optical signal splitter/combiner 334 where the amplified first opticalwavelength band signal portion 102A is combined with the amplifiedsecond optical wavelength band signal portion 102B. The combined signalpasses through the optical circulator 338 and into the GFF 342. In someimplementations the GFF 342 may pass optical frequencies falling withinboth the first optical wavelength band signal portion 102A and thesecond optical wavelength band signal portion 102B and reject otheroptical frequencies.

The GFF 342 reflects at least a portion of the first optical wavelengthband signal portion 102A_(r) and a portion of the second opticalwavelength band signal portion 102B_(r). The reflected first opticalwavelength band signal portion 102A_(r) and second optical wavelengthband signal portion 102B_(r) enter the four-port type-2, optical signalsplitter/combiner 334 where the reflected first optical wavelength bandsignal portion 102A_(r) enters an optical amplifiers 1402. The opticalamplifier 1402 may include a co-pumped stage 1404 and a counter-pumpedstage 1406 that feed the erbium doped fiber coil 1408.

In embodiments the optical amplifier 1402 may amplify some or all of thewavelengths in the second optical wavelength band signal portion 102B.In some implementations, the optical amplifier 1402 may be selected,operated, and/or tuned such that the gain of at least the second opticalwavelength band signal portion 102B is sufficient and additionalamplification of the second optical wavelength band signal portion 102Bmay be unnecessary. In embodiments, the optical amplifier 1402 mayinclude at least one erbium doped fiber amplifier (EDFA). Inembodiments, the optical amplifier 1402 may include at least oneco-pumped amplifier stage 1404 and at least one counter-pumped amplifierstage 1406. In embodiments, the co-pumped amplifier stage 1404 and thecounter-pumped amplifier stage 1406 may feed the same erbium doped fibersegment 1408. In other embodiments, the co-pumped amplifier stage 1404and the counter-pumped amplifier stage 1406 may feed different erbiumdoped fiber segments (not shown in FIG. 14). The optical amplifier 1402may be operably coupled to a single EDFA pump source 708 that includesat least one EDFA pump 710 and at least one optical splitter 712 may beused to power the optical amplifier 1402. Various configurations forEDFA pump sources that may be controlled locally or remotely are knownto those of ordinary skill in the art. Also, the pump sources may becoupled to the optical path 320 in any known configuration.

FIG. 15 is a high-level flow diagram of an illustrative amplificationand reflected signal energy recovery method 1500, in accordance with atleast one embodiment of the present disclosure. In at least someimplementations, an incoming optical signal 102 may include at least afirst optical wavelength band signal portion 102A and a second opticalwavelength band signal portion 102B. As part of the amplificationprocess, the incoming optical signal 102, the first optical wavelengthband signal portion 102A, and/or the second optical wavelength bandsignal portion 102B may pass through one or more gain flattening filters(GFFs). At least a portion of the first optical wavelength band signalportion 102A_(r) may be reflected by the one or more GFFs. At least aportion of the energy carried by this reflected portion of the firstoptical wavelength band signal portion 102A_(r) may be recovered andused to amplify or otherwise increase the gain of the second opticalwavelength band signal portion 102B. The reuse of energy in thereflected first optical wavelength band signal portion 102A_(r)beneficially reduces the external energy supply requirements by acommensurate amount. Over the course of an extended opticalcommunication run, significant power savings may be realized. The method1500 commences at 1502.

At 1504, the incoming optical signal may be apportioned or otherwisesplit or divided into at least a first optical wavelength band signalportion 102A and a second optical wavelength band signal portion 102B.In some implementations, the incoming signal 102 may be split orotherwise apportioned using one or more three-port or four-port opticalsignal splitter/combiners. In at least some implementations, the one ormore three-port or four-port optical signal splitter/combiners may bebased on a dielectric thin film filter (TFF).

In embodiments, the one or more three-port or four-port optical signalsplitter/combiners may include one or more type-1 optical signalsplitter/combiners that transmit all or a portion of the first opticalwavelength band signal portion 102A and reflect all or a portion of thesecond optical wavelength band signal portion 102B. In embodiments, theone or more three-port or four-port optical signal splitter/combinersmay include one or more type-2 optical signal splitter/combiners thattransmit all or a portion of the second optical wavelength band signalportion 102B and reflect all or a portion of the first opticalwavelength band signal portion 102A.

At 1506, the second optical wavelength band signal portion 102B may passthrough one or more amplifiers that amplify or otherwise increase thegain of the second optical wavelength band signal portion 102B. Inembodiments, the one or more amplifiers may amplify some or all of thewavelengths in the second optical wavelength band signal portion 102B.In some implementations, the one or more amplifiers may be selected,operated, and/or tuned such that no additional amplification of thesecond optical wavelength band signal portion 102B is needed.

In embodiments, the one or more amplifiers may include one or moreerbium doped fiber amplifiers (EDFAs). Each of the EDFAs may include asingle or multi-stage EDFA, and may include one or more EDFA pumpsources, a coupler, and an erbium-doped fiber segment. Variousconfigurations for EDFA pump sources that may be controlled locally orremotely are known to those of ordinary skill in the art. Also, the pumpsources may be coupled to the optical path in any known configuration.

At 1508, the first optical wavelength band signal portion 102A and theamplified second optical wavelength band signal portion 102B arecombined. In some implementations, the first optical wavelength bandsignal portion 102A and the amplified second optical wavelength bandsignal portion 102B may be combined using one or more type-1 three-portor four-port optical signal splitter/combiners and/or one or more type-2three-port or four-port optical signal splitter/combiners.

At 1510, the combined first optical wavelength band signal portion 102Aand the amplified second optical wavelength band signal portion 102B maybe filtered through one or more GFFs.

At 1512, at least a portion of the incident first optical wavelengthband signal portion 102A_(r) may be reflected by the one or more GFFs.

At 1514, the one or more amplifiers used to amplify or otherwiseincrease the gain of the second optical wavelength band signal portion102B may use at least a portion of the energy carried by the reflectedfirst optical wavelength band signal portion 102A_(r) to amplify orotherwise increase the gain of the second optical wavelength band signalportion 102B. The method 1500 concludes at 1516.

FIG. 16 is a high-level flow diagram of an illustrative amplificationand reflected signal energy recovery method 1600 that may be used inconjunction with all or a portion of the method 1500 depicted in FIG.15, in accordance with at least one embodiment of the presentdisclosure. The illustrative amplification and reflected signal energyrecovery method 1600 amplifies an incoming optical signal 102 prior tosplitting the incoming optical signal into at least a first opticalwavelength band signal portion 102A and a second optical wavelength bandsignal portion 102B. Such an amplification may, for example, occur priorto 1504 as depicted in FIG. 15.

In some implementations, the first optical wavelength band signalportion 102A may be amplified prior to splitting the first opticalwavelength band signal portion 102A and the second optical wavelengthband signal portion 102B. The method 1600 commences at 1602.

At 1604, the first optical wavelength band signal portion 102A may beamplified prior to splitting the first optical wavelength band signalportion 102A and the second optical wavelength band signal portion 102B.In at least some implementations, the incoming signal 102 that includesat least the first optical wavelength band signal portion 102A and thesecond optical wavelength band signal portion 102B may be amplifiedprior to splitting the incoming signal 102 into the first opticalwavelength band signal portion 102A and the second optical wavelengthband signal portion 102B. The method 1600 concludes at 1606.

FIG. 17 is a high-level flow diagram of an illustrative amplificationand reflected signal energy recovery method 1700 that may be used inconjunction with all or a portion of the method 1500 depicted in FIG.15, in accordance with at least one embodiment of the presentdisclosure. The illustrative amplification and reflected signal energyrecovery method 1700 amplifies a first optical wavelength band signalportion 102A of an incoming optical signal 102 subsequent to splittingthe incoming optical signal 102 into at least the first opticalwavelength band signal portion 102A and a second optical wavelength bandsignal portion 102B. In embodiments, such amplification of the firstoptical wavelength band signal portion 102A of the incoming opticalsignal 102 may occur prior to, concurrent with, or subsequent to 1506 asdepicted in FIG. 15. The method 1700 commences at 1702.

At 1704, the incoming optical signal 102 may be split or otherwiseapportioned into a first optical wavelength band signal portion 102A anda second optical wavelength band signal portion 102B using one or moretype-1 three-port or four-port optical signal splitter/combiners and/orone or more type-2 three-port or four-port optical signalsplitter/combiners. Subsequent to splitting the incoming optical signal102 into the first optical wavelength band signal portion 102A and thesecond optical wavelength band signal portion 102B, the first opticalwavelength band signal portion 102A and the second optical wavelengthband signal portion 102B may be separately amplified using one or moreamplifiers. The method 1700 concludes at 1706.

FIG. 18 is a high-level flow diagram of an illustrative amplificationand reflected signal energy recovery method 1800, in accordance with atleast one embodiment of the present disclosure. In at least someimplementations, an incoming optical signal 102 may include at least afirst optical wavelength band signal portion 102A and a second opticalwavelength band signal portion 102B. As part of the amplificationprocess, the incoming optical signal 102, the first optical wavelengthband signal portion 102A, and/or the second optical wavelength bandsignal portion 102B may pass through one or more gain flattening filters(GFFs). At least a portion of the first optical wavelength band signalportion 102A_(r) may be reflected by the one or more GFFs. At least aportion of the energy carried by this reflected portion of the firstoptical wavelength band signal portion 102A_(r), may be recovered andused to amplify or otherwise increase the gain of the second opticalwavelength band signal portion 102B. The reuse of energy in thereflected first optical wavelength band signal portion 102A_(r)beneficially reduces the external energy supply requirements by acommensurate amount. Over the course of an extended opticalcommunication run, significant power savings may be realized. The method1800 commences at 1802.

At 1804, an optical signal that includes at least a first opticalwavelength band signal portion 102A and a second optical wavelength bandsignal portion 102B may be passed through one or more amplifiers.

At 1806, the amplified optical signal may be passed through one or morefilters. In at least some implementations, the one or more filters mayinclude one or more gain flattening filters (GFFs).

At 1808, the one or more filters reflect at least a portion of the firstoptical wavelength band signal portion 102A_(r). At least a portion ofthe reflected first optical wavelength band signal portion 102A_(r) maybe received by the one or more amplifiers used to amplify the firstoptical wavelength band signal portion 102A and a second opticalwavelength band signal portion 102B.

At 1810, at least some of the energy carried by the reflected portion ofthe first optical wavelength band signal portion 102A_(r) may be used bythe one or more amplifiers to amplify or otherwise increase the gain ofthe second optical wavelength band signal portion 102B. The method 1800concludes at 1812.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention,in the use of such terms and expressions, of excluding any equivalentsof the features shown and described (or portions thereof), and it isrecognized that various modifications are possible within the scope ofthe claims. Accordingly, the claims are intended to cover all suchequivalents.

What is claimed:
 1. An optical communication amplification system,comprising: an optical splitter to separate an optical signal into atleast a first optical wavelength band signal portion and the secondoptical wavelength band signal portion; an optical amplifier operablycoupled to the optical splitter, the optical amplifier to increase theenergy of the second optical wavelength band signal portion; an opticalcombiner that combines the first optical wavelength band signal portionand the amplified second optical wavelength band signal portion; and anoptical filter operably coupled to the optical combiner, wherein aportion of the energy of the first optical wavelength band signalportion reflected from the optical filter is received by the opticalamplifier where the received energy increases the energy of the secondoptical wavelength band signal portion.
 2. The system of claim 1,further comprising: an optical amplifier that receives the opticalsignal and increases the energy of at least the first optical wavelengthband signal portion of the received optical signal.
 3. The system ofclaim 2, further comprising: a first optical isolator operably coupledto an input of the optical amplifier that increases the energy of atleast the first optical wavelength band signal portion of the receivedoptical signal.
 4. The system of claim 2 wherein the optical amplifierthat increases the energy of at least the first optical wavelength bandsignal portion of the received optical signal comprises a C-band/L-banderbium doped fiber amplifier (C/L-EDFA).
 5. The system of claim 1,further comprising: an optical amplifier disposed subsequent to theoptical splitter to receive the first optical wavelength band signalportion and increase an energy level of the first optical wavelengthband signal portion.
 6. The system of claim 1, further comprising: anoptical circulator having a first port operably coupled to the opticalcombiner, a second port operably coupled to the optical filter, and athird port operably coupled the optical combiner such that at least aportion of the energy of the reflected first optical wavelength bandsignal portion reflected from the optical filter is provided to thesecond amplifier.
 7. The system of claim 1 wherein the energy of thesecond optical wavelength band signal portion reflected from the opticalfilter is provided to the optical splitter.
 8. The system of claim 1,further comprising: an optical isolator operably coupled to the opticalamplifier that increases the energy of the second optical wavelengthband signal portion.
 9. The system of claim 1: wherein the first opticalwavelength band signal portion comprises a C-band; wherein the secondoptical wavelength band signal portion comprises an L-band; and whereinthe optical amplifier that increases the energy of the second opticalwavelength band signal portion comprises a C-band/L-band erbium dopedfiber amplifier (C/L-EDFA).
 10. The system of claim 9 wherein theoptical splitter comprises a three-port C-band/L-band opticalde-multiplexer that transmits the C-band wavelength signal portion andreflects the L-band wavelength signal portion.
 11. The system of claim10 where in the optical combiner comprises a four-port C-band/L-bandoptical multiplexer that reflects the C-band wavelength signal portionand transmits the L-band wavelength signal portion.
 12. The system ofclaim 9 wherein the optical filter comprises a gain flattening filter(GFF).
 13. The system of claim 12 wherein the GFF comprises a ShortPeriod Fiber Bragg Grating GFF.
 14. An optical communicationamplification method, comprising: splitting an optical signal into afirst optical wavelength band signal portion and a second opticalwavelength band signal portion; amplifying, via an optical amplifier,the second optical wavelength band signal portion of the optical signal;combining the first optical wavelength band signal portion and theamplified second optical wavelength band signal portion to provide anamplified optical signal; filtering, via at least one optical filter,the amplified optical signal; receiving, by the optical amplifier, atleast a portion of the first optical wavelength band signal portionreflected by the at least one optical filter, and increasing the energyof the optical amplifier using energy in the reflected portion of thefirst optical wavelength band signal portion.
 15. The method of claim14, further comprising: amplifying, via an optical amplifier, at leastthe first optical wavelength band signal portion of the optical signalprior to splitting the optical signal into the first optical wavelengthband signal portion and the second optical wavelength band signalportion.
 16. The method of claim 14, further comprising: amplifying, viaan optical amplifier, at least the first optical wavelength band signalportion of the optical signal subsequent to splitting the optical signalinto the first optical wavelength band signal portion and the secondoptical wavelength band signal portion.
 17. The method of claim 14wherein splitting an optical signal into a first optical wavelength bandsignal portion and a second optical wavelength band signal portioncomprises: splitting the optical signal into a C-band signal portion andan L-band portion signal using a three-port, C-band/L-band, wavelengthdivision demultiplexer.
 18. The method of claim 17 wherein amplifying,via an optical amplifier, the second optical wavelength band signalportion of the optical signal comprises: amplifying the L-band signalportion of the optical signal using an L-band erbium doped fiberamplifier (L-EDFA).
 19. The method of claim 18 wherein combining thefirst optical wavelength band signal and the amplified second opticalwavelength band signal to provide an amplified combined optical signalcomprises: combining the C-band signal portion and the amplified L-bandsignal portion to provide an amplified optical signal using a four-port,C-band/L-band, wavelength division multiplexer.
 20. The method of claim19 wherein filtering, via at least one optical filter, the amplifiedoptical signal comprises: filtering, via at least one Gain FlatteningFilter (GFF), the amplified optical signal.
 21. The method of claim 20wherein filtering, via at least one Gain Flattening Filter (GFF), theamplified optical signal comprises: filtering, via at least one ShortPeriod Fiber Bragg Grating, the amplified optical signal.
 22. The methodof claim 20 wherein reflecting at least a portion of the first opticalwavelength band signal portion of the amplified optical signal from theat least one optical filter comprises: reflecting at least a portion ofthe C-band signal portion of the amplified optical signal from the atleast one GFF.
 23. The method of claim 19 wherein increasing the energyof the optical amplifier using energy in the reflected portion of thefirst optical wavelength band signal portion reflected by the at leastone optical filter comprises: increasing the energy of the L-EDFA usingenergy in the reflected portion of the C-band signal portion reflectedby the at least one GFF.
 24. An optical communication amplificationmethod, comprising: amplifying, by an optical amplifier, an opticalsignal that includes at least a first optical wavelength band signalportion and a second optical wavelength band signal portion; passing theamplified optical signal through at least one optical filter; receiving,at the optical amplifier, at least a portion of energy in the firstoptical wavelength band signal portion reflected by the at least oneoptical filter; and increasing the energy of an optical amplifier usedto increase the energy level of the second optical wavelength signalportion using the reflected energy in the first optical wavelengthsignal portion.
 25. The method of claim 24 wherein amplifying an opticalsignal that includes at least a first optical wavelength band signalportion and a second optical wavelength band signal portion comprises:amplifying, via an erbium doped fiber amplifier, the optical signal thatincludes at least a C-band signal portion and an L-band signal portion.26. The method of claim 25 wherein increasing the energy of an opticalamplifier used to increase the energy level of the second opticalwavelength band signal portion using the reflected energy in the firstoptical wavelength band signal portion comprises: increasing the energyof an erbium doped fiber amplifier used to increase the energy level ofthe L-band signal portion using the reflected energy in the C-bandsignal portion.